This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. Primary support for the subproject and the subproject's principal investigator may have been provided by other sources, including other NIH sources. The Total Cost listed for the subproject likely represents the estimated amount of Center infrastructure utilized by the subproject, not direct funding provided by the NCRR grant to the subproject or subproject staff. Beta-lactams are the most common antibiotics in clinical use and represent more than 60% of total world consumption of antimicrobial drugs. They include penicillins, cephalosporins, monobactams, penems and carbapenems, and over 50 antibiotics of this class are available on the market. A major mechanism of bacterial resistance to beta-lactam antibiotics is the production of beta-lactamases, enzymes that hydrolyze the conserved four-membered ring of beta -lactams in a two-step process. We are working on three recently-discovered beta -lactamase enzymes. The first, named GES-1 (Guiana Extended-Spectrum, after the country where it was first isolated) was initially described in 2000. This extended spectrum beta -lactamase (ESBL) is very distantly related to other class A beta -lactamases and produces resistance to penicillins and first-, second-, and some third-generation cephalosporins (e.g. ceftazidime) but not to monobactams and carbapenems. Since 2000, nine GES-type enzymes (GES-1 - GES-9) from different geographical locations have been described. The most alarming characteristic of the GES family of enzymes that distinguish them from the TEM and SHV superfamilies, is their apparent ability to evolve into weak carbapenemases, enzymes capable of hydrolyzing carbapenem antibiotics. We will systematically pursue structures of these systems.